1. Field of the Invention
The invention concerns a measuring device for carrying out luminescence measurements of fluid samples.
2. Description of the Related Art
Measurement devices of this type are employed primarily in automatic or semi-automatic operated analytic instruments for sequential analytic analysis of chemical and biological systems. The principle of measurement is based upon the detection of a light signal, which is emitted by a reaction partner taking part in a chemiluminescence reaction or by a substance which is stimulated to fluoresce by activation light. Therein even very weak light signals can be measured with high precision with highly sensitive light detectors such as photomultipliers, so that in principle a high detection sensitivity is obtainable.
In known measuring devices of the type described above, an orifice plate is used to interface the inlet cross-section of the photomultiplier to the opening diameter of the sample vessels, which are provided in a matrix-like manner in a micro-test-plate. The orifice plate is provided as a stationary orifice plate, of which the orifices expose the measurement openings of the thereunder situated sample vessels, while the remaining sample vessels are covered over in the upper side with respect to the light detector. It has been found to be disadvantageous therein, that even the smallest gap in the area between the micro-test-plate and the orifice plate suffices to substantially compromise the measurement sensitivity. This is due to the fact that stray light, above all the so-called transference between the individual sample vessels, is diffused via such gaps into the inlet cross-section of the photomultiplier. In addition to this there is the problem that fluorescence of samples in the adjacent vessels may in this manner be triggered prematurely.